The Holocaust Encyclopedia reveals to the reader one of the most terrible pages of the 2nd World War of 1939-45. - the history of the mass extermination by the Nazis of Jews, Gypsies, as well as representatives of a number of social groups (mentally ill, homosexuals, etc.). In our country, this aspect of the world tragedy has been hushed up by the authorities and official historiography for many decades. Prepared under the scientific supervision of the American historian Walter Lacoeur, the book is the fruit of the collective work of over 100 authors from 11 countries. Articles in it were written by both Jews and non-Jews, scientists and witnesses of events, young people who grew up in peacetime, and people of the older generation who went through the hell of Hitler's camps.